Analog Devices Inc. AD7828LRS

Overview

AD7828LRS from Analog Devices is an 8-channel, 8-bit LC2MOS successive-approximation analog-to-digital converter with built-in track-and-hold, single 5 V supply operation, ±1/2 LSB total unadjusted error, and 2.5 µs per-channel conversion time. It digitizes 0 V to 5 V analog inputs across eight multiplexed channels and is used in real-time data acquisition systems for industrial monitoring and speech analysis.

For engineers reviewing the AD7828LRS datasheet, AD7828LRS pinout, AD7828LRS application, or AD7828LRS equivalent, key selection criteria include its 8-channel multiplexer address decoding (A0–A2), open-drain RDY/INT outputs, 28-pin RS-28 DIP package, and compatibility with Z80, MC68000, and TMS32010 microprocessor interfaces without external clocking.

Technical Context

The AD7828LRS employs a half-flash architecture using two 4-bit flash ADCs-one for MSBs and one for LSBs-combined with an internal 4-bit DAC to reconstruct and subtract the MSB analog approximation, enabling full 8-bit resolution without external timing. Its analog input structure inherently performs sample-and-hold over ~1 µs, supporting 10 kHz full-scale sinusoidal inputs (157 mV/µs slew rate) on all eight channels.

It operates in Mode 0 (WAIT-state microprocessors) or Mode 1 (non-WAIT), with CS/RD-controlled conversion initiation and three-state DB0–DB7 data outputs. The RDY output is open-drain and requires an external pull-up; INT asserts low upon conversion completion and resets on rising edges of CS or RD.

Key Specifications

Pinout & Package

AD7828LRS is housed in a 28-pin RS-28 plastic dual-in-line package (0.6" wide), compliant with JEDEC MS-011AB. Pin 1 is identified by a notch or dot; pins are numbered counterclockwise from top-left when viewed from top.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 8-channel, 8-bit ADC applications.

Compared with AD7828LN, AD7828LRS offers improved lead coplanarity for automated insertion, while MAX1138CPI+ trades parallel simplicity for serial integration-neither provides drop-in replacement capability due to package or interface incompatibility.

Availability

AD7828LRS is available at Aetrix Electronics and suitable for industrial process monitoring, speech analysis systems, embedded data loggers, test & measurement front-ends, and real-time signal acquisition requiring stable component supply and long-term obsolescence management.

Supply support for AD7828LRS includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Analog Devices, Inc. is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, founded in 1965 and headquartered in Wilmington, MA.

The AD7828LRS belongs to Analog Devices' legacy LC2MOS precision data acquisition product line, designed specifically for cost-sensitive, microprocessor-based multichannel measurement systems requiring fast conversion, low power, and simple parallel interfacing.

FAQ

What is the maximum analog input frequency supported by the AD7828LRS without external sample-and-hold?

The AD7828LRS supports full-scale sinusoidal inputs up to 10 kHz (157 mV/µs slew rate) on any channel without external sample-and-hold, thanks to its inherent track-and-hold function active for ~1 µs after conversion start. This is confirmed in the "SINUSOIDAL INPUTS" section of the datasheet, where it states the device can measure eight 10 kHz signals directly. The AD7828LRS achieves this via its half-flash architecture and input capacitor switching behavior.

Does the AD7828LRS require an external clock signal to operate?

No, the AD7828LRS does not require an external clock signal. Its half-flash conversion technique uses internal timing derived from CS and RD control signals only. As stated in the "GENERAL DESCRIPTION", "there is no need to generate a clock signal for the ADC", and the "TIMING AND CONTROL" section confirms all timing is governed by tCRD, tP, and handshaking signals. This simplifies system design and eliminates clock distribution noise concerns for the AD7828LRS.

What is the meaning of the "L" grade in AD7828LRS, and how does it affect performance?

Per the Ordering Guide, the "L" grade in AD7828LRS denotes ±1/2 LSB total unadjusted error (vs. ±1 LSB for "K" grade) across the 0°C to +70°C commercial temperature range. This tighter error spec guarantees monotonicity and no missing codes without calibration, making the AD7828LRS suitable for applications demanding higher linearity-such as precision sensor readout-where the base AD7828KN would require post-fabrication trimming. All other electrical parameters remain identical to the K grade.

How is the RDY pin configured, and what external components are needed for proper operation?

The RDY pin on the AD7828LRS is an open-drain output requiring an external pull-up resistor to VDD (typically 4.7 kΩ to 5 V). As noted in the "TIMING CHARACTERISTICS" table and "MODE 0" description, RDY goes low on the falling edge of CS and transitions to high-impedance at conversion completion to signal data validity. If RDY is unused, the datasheet permits tying it directly to GND-but doing so forfeits ready-status feedback, forcing fixed-delay polling instead of efficient handshaking for the AD7828LRS.

Can the AD7828LRS be used in bipolar input configurations, and if so, how?

Yes, the AD7828LRS supports bipolar operation via external signal conditioning. Figure 12 shows a circuit using an AD544 op amp to shift and scale ±4 V inputs into the 0 V to 5 V unipolar range accepted by the AD7828LRS analog inputs. The differential reference inputs (VREF+, VREF−) allow offsetting the zero point, and the output code becomes complementary offset binary. This configuration is validated in the "BIPOLAR OPERATION" section and enables true bipolar measurement without modifying the AD7828LRS itself.